A female who is, in one manner or another, completely obsessed with anime, manga, and generally all things having to do with japan. They generally focus on these things to the exclusion of all else, including getting laid.

The Anime Eletists or Anime Leet. People with years of "expirience" in anime-watching. To be an otaku, you must have at least 5 years of watching, 300 series & OAVs watched, more than half of them have to be subtitled or raw, you have to own at least 1 fansub, 1 ufo catcher doll, 1 doujinshi, 1 untranslated manga, 1 shitajiki, been to at least 1 con in full cosplay, one anime ost, knowledge of Japanese popular subcultures, a fleet of Japanese slang words, plus the ability to read katakana, hiragana, & instantly reccognize a few kanjis.

Someone who only watches dubbed anime on TV or borrows dubbs from their friends will never become Otaku.

Otakus have little to no tollerance for noobs, but will take one under their wing & teach them how to properly enjoy all Japan has to offer.

An anime fan is just a n00b, but an otaku is l33t. (noob/newbie) (leet/elite).